Liquid crystal panels, by reason of their small thickness and lightweight, have been widely used for display devices such as a television receiver, a display device for a computer, and a display section of a personal digital assistant. Since liquid crystals, however, take a certain time to reach a designated transmittance after the driving voltage is applied thereto, there has been a shortcoming in that the liquid crystals cannot respond to motion images changing quickly. In order to solve such a problem, a driving method is employed in which an overvoltage is applied to a liquid crystal so that the liquid crystal reaches a designated transmittance within one frame in a case of gray-scale values varying frame by frame (Japanese Patent Publication No. 2616652). To be more specific, comparing on a pixel to pixel basis current-frame image data with image data preceding by one frame, if a gray-scale value varies, a compensation value corresponding to the variation is added to the current-frame image data. That is, if a gray-scale value increases with respect to that preceding by one frame, a driving voltage higher than usual is applied to the liquid crystal panel, and if decreases, a voltage lower than usual is applied thereto.
In order to perform the method described above, a frame memory is required to output image data preceding by one frame. Recently, there has been a need for increasing capacity of a frame memory with increasing pixels to be displayed due to upsizing of liquid crystal panels. Moreover, since increase in the number of pixels to be displayed involves to increase the amount of data to be read from and written into a frame memory during a given period (for example, one frame period), a data transfer rate needs to be increased by increasing the clock frequency that controls the reading and writing. Such increase in capacity of frame memory and in the transfer rate leads to cost increase of liquid crystal display devices.
In order to solve such problems, the image processing circuit for driving a liquid crystal, disclosed in Japanese Laid-Open Patent Publication No. 2004-163842, reduces its frame memory capacity by encoding image data to be stored therein. By correcting image data based on a difference between decoded image data of a current frame obtained by decoding encoded image data and image data preceding by one frame obtained by decoding encoded image data delay by one frame period, unnecessary voltage caused by an encoding and decoding error, which occurs when a still image is inputted, can be prevented from being applied to the liquid crystal.